Gray scale images of various documents are often stored on microfilm for subsequent retrieval in order to conserve storage space by advantageously eliminating the need to store bulky paper originals. Retrieving (accessing) a microfilmed image of a document, on a manual basis, typically requires locating a desired roll of microfilm that houses the desired image, loading the roll into a manual reader and then advancing the microfilm to a desired frame at which the image is located. Thereafter, the image is optically enlarged and displayed on the reader.
Now, to minimize image retrieval time, particularly for archives that store a substantial number of documents, and also to permit the retrieved image to be electronically enhanced and processed, image management systems have been developed in the art. These systems are typified, for example, by the Kodak Image Management System (KIMS) system currently manufactured by the present assignee (KIMS is a trademark of the Eastman Kodak Company). Essentially, the KIMS system first locates the desired microfilm roll and frame through a computerized database inquiry. Then, an automated microfilm reader, i.e. a so-called film library also known as an autoloader, operating under computer control, fetches and then loads the desired roll into the reader. Once this has occurred, the film library automatically advances the roll to the desired frame. Thereafter, the film library electronically scans and digitizes a gray scale microfilm image present at the desired frame typically at a resolution of 300-400 dots/inch (approximately 118-157 dots/centimeter--cm), and finally applies the resulting digitized bi-tonal image onto a local area network for storage, display and/or printing at an appropriate node within the system.
An image management system, such as the KIMS system, generally contains several different nodes interconnected through a local area network and connected through a wide area network to other processing equipment, such as illustratively a host computer. Each such node, depending upon its sophistication, illustratively provides one or more image processing and/or network functions; for example, paper or film scanning, image printing, image display, file serving, and/or an interface to the wide area network. A document workstation typically serves as one of these nodes. Typically, a user of such an image management system enters commands to the system through a document workstation and in response receives displayed images in one form or another therefrom. The workstation transmits commands through local and/or wide area network connections from the user to a suitable node within the system or to an external host processor and thereafter receives appropriate compressed image data therefrom.
Frequently, the user of an image management system can readily identify a particular file of related images but can not readily identify which specific image he or she needs without first examining each image in that file. In particular, through the workstation, the user selects a given image file by examining successive portion(s) of a computer based cross-reference file resident on, for example, a host computer until he or she locates the image file of interest. Once this image file is located, the user, through the workstation, can command the host computer to download microfilm roll and frame numbers associated with all the images contained within the selected image file to the film library connected to a scanner node, then instruct the film library to sequentially access, scan, digitize and compress each image in the file and finally transfer each resulting compressed image over a local and/or wide area network connection(s) to the workstation for local display thereat. The user would then be required to observe each successive resulting image that appeared on the workstation until the specific image(s) he or she wanted was displayed. Unfortunately, by forcing the user to successively examine each image in the image file, a significant burden is placed on the user which frustrates the user and tends to greatly waste his or her time, particularly where the image file contains more than just a very small number of images.
Consider, for example, an image management system that stores image files of related documents for insurance claims. Such an image file associated with a single claim for property damage may contain illustratively 15-20 separate images of which some images may depict a claim form, other images may depict a report(s) from an insurance adjuster that documents property damage and so on for all other related documentation in the file. Accordingly, if a user sought to obtain an image of a specific item, such as the last item, contained within this particular image file, that user would be forced to wait until all the images for all preceding items in this file were successively displayed. Inasmuch as each image, depending upon its content, may take upwards of at least several seconds to be fully displayed at the workstation, the user could be waiting a minute or more until the particular image he or she wanted was displayed. If a wait of this or a similar duration were to be experienced by the user each time he or she accessed an image file, the user would likely waste a significant amount of time and become quite frustrated at the apparent slow response time of the image management system.
The vast majority of the images stored within an image management system tends to be of textual documents that may, as in the case of forms, also contain line art. Such textual images are bi-tonal in nature and predominantly contain background color with interspersed patterns of foreground color associated with textual characters and/or line art. The background color is usually either black or white with the foreground color being opposite in nature, i.e. respectively either white or black. The vast majority of the pixels that form any such textual image takes on the background color. After being digitized, the textual images are well thresholded but do not contain dithering or error diffusion.
One way to reduce the time required of a user to examine separate images in an image file would be to simultaneously display a number of these images at a document workstation, each at a reduced size in, for example, a corresponding non-overlapping portion of a composite multi-image display. As such, the display would resemble a grid of separate images, with each image being displayed at a reduced scale. The grid may illustratively contain 16 or 20 such images situated in separate corresponding cells contained within, for example, a common 4-by-4 or 4-by-5 matrix that fills a display screen. Once the composite display fully appeared on the display screen, the user could then very quickly glance through the entire display and select a particular image(s) he or she wanted for subsequent display at full scale. Advantageously, all the operations including the formation and depiction of the composite display at the workstation, image selection by the user and ultimate full scale display of the selected image(s) at the workstation would occur within a much shorter interval of time than that which would otherwise be required to successively display each image in the matrix at full scale.
Various techniques exist in the art to scale, specifically reduce, bi-tonal images. Unfortunately, for one reason or another, none of these techniques has proven to be completely satisfactory for use in forming composite images for display at a workstation in an image management system. Generally, though not always, these prior art techniques involve use of either convolution or two dimensional interpolation. For example, U.S. Pat. No. 4,829,587 (issued to Glazer et al on May 9, 1989) describes apparatus for re-scaling an image that relies on assembling sets of pixel values from an original image into sub-matrices and thereafter convolving the sub-matrices to compute scaled pixel values. This apparatus appears to be rather complex to implement. Another approach described in U.S. Pat. No. 4,302,776 (issued to Taylor et al on Nov. 24, 1981) relies on interpolating pixel values from an original image in both horizontal and vertical directions to yield a scaled image. A second interpolation based scaling technique is described in both U.S. Pat. Nos. 4,532,602 and 4,587,621 (both issued to DuVall on July 30, 1985 and May 6, 1986, respectively). This technique relies on interpolating between pairs of pixel values to provide a scaled pixel value. Unfortunately, interpolation techniques tend to be arithmetically intensive and, as such, usually require an excessive number of clock cycles to process incoming pixel data. Consequently, interpolation based techniques tend to disadvantageously reduce the speed at which a multi-image composite display could be depicted by a document workstation, thereby limiting the throughput at which such images can be displayed by an image management system.
Another scaling technique, involving neither convolution or interpolation, is described in U.S. Pat. No. 4,610,026 (issued to Tabata et al on Sept. 2, 1986). This particular technique relies on determining each pixel value in a scaled image from a matrix of pixel values in an original image through use of periodicities that occur between corresponding image elements situated in the matrix in an original image and a corresponding matrix of pixels in a scaled image as defined by scale factor or magnification ratios occurring therebetween as well as from the pixel values in the matrix in the original image. Unfortunately, this technique also appears to be quite complex to implement.
Inasmuch as scaling techniques known in the art generally attempt to preserve as much image detail that resides in an original image as possible in an output image scaled therefrom, these prior art techniques, such as illustratively those specifically discussed above, tend to be complex to implement and/or consume an inordinate amount of processing time to perform. For these reasons, such techniques are not ideally suited for use in fabricating a composite multi-image display for display in an image management system.
Nevertheless, it is generally recognized in the art that a human eye can quickly recognize the overall content of a displayed image even though that image contains a considerable loss of detail. Accordingly, a composite multi-image display, which is to be used in an image management system and is merely displayed to allow a user to select among its constituent reduced images, can contain a significant amount of error as long as sufficient visual information remains in each reduced image to enable the user to quickly and grossly recognize the overall content of that image. Therefore, in providing such a composite image for display in an image management system, the need to preserve image detail becomes quite subservient to the need to provide a scaling technique that is relatively simple and inexpensive and performs image reduction relatively fast.
Therefore, a need exists in the art for a scaling technique that is useful in forming scaled, specifically reduced, versions of original images for display by an image management system and which is relatively simple and inexpensive to implement and is capable of producing scaled images within a minimal amount of processing time. The technique should operate with original images that generally contain textual and/or line art material, are predominantly background with essentially no dithering or error diffusion and are well thresholded. Furthermore, the technique should not be constrained to preserving considerable amounts of fine image detail in each scaled image but instead can produce scaled images that, in fact, contain a considerable loss of detail provided that the detail that remains in each scaled image is generally sufficient to permit a user to quickly recognize the overall content of that scaled image.